Ignitron starter



June 18, 1940.

J. SLEPIAN IGNITRON STARTER Filed Aug. 12, 1958 w m D n WITNESSES:

ATTORNE Patented June 18, 1940 UNITED STATES IGNITRON STARTER Joseph Slepian,

Pittsburgh, Pa.,

assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application August 12, 1938, Serial No. 224,520

4 Claims.

This invention relates to vapor-arc electric discharge devices and more particularly to electrodes employed therein for initiating the formation of an arc.

5 In connection with cold cathode vapor-arc discharge devices, the initiation of the arc discharge may be obtained by constant excitation of an auxiliary electrode. However, improved operation and more advantageous control characteristics result from cathode spot formation at conductive cycles of vapor-arc converters, such as mercury rectifiers. By the latter method of operation, the cathode spot is extinguished at the end of each conducting cycle and restored at the 16 beginning of the next successive conducting period. The former method of operation whereconstant excitation of the auxiliary electrode is maintained is generally referred to as keep-alive excitation by a keep-alive electrode whereas the 20 latter improved method of operation, as distinguished from the previous one, is known as makealive excitation by a make-alive electrode. The type of discharge devices operated in such manher are known as Ignitron or Vectron, and are described in U. S. Patent No. 2,069,283.

In the Ignitron type rectifiers, to which this invention is directed, the igniting electrode hereinafter referred to as the make-alive electrode, in order to initiate the arc, must create a cathode spot. To this end, a direct physical contact between cathode and make-alive electrode is necessary and the latter is usually immersed in the mercury pool type cathode, and must be of a suitable resistance material to limit the starting current. At the same time, the electrode must also be of such material which will not form mercurial amalgamation. Heretofore, the most suitable make-alive electrode material used was carborundum, preferably in crystal form, although it has the marked disadvantage of requiring a high current to initiate the cathode spot, and has the tendency to amalgamate with the cathode material especially if subjected to inverse current 45 flow due to failure of the control apparatus. Other materials of an improved character for make-alive electrode structure were found'to be boron and boron carbide.

The primary object of the present invention is 50 to construct the make-alive electrode of a resistance material having a negative temperature coefficient which exhibits marked advantages" over those previously used, is simple to manufacture in any desired resistive density.

55 A further object of this invention is to utilize the properties of uranium dioxide (U02) as a resistance material for make-alive electrodes.

Other objects and advantages will be apparent from the following description of the invention, pointed out in particularity by the appended claims, and taken in'connection with the accompanying drawing in which:

.Figure 1 is a view showing one form which the electrode may take when applied to a certain type of Ignitron rectifiers.

Fig. 2 illustrates by way of example the type of Ignitron rectifier in which the electrode form of Fig. 1 may be utilized.

The invention herein described is directed to the particular composition of matter useful in general application as a starting electrode of various gaseous discharge devices. The shape,- size and consistency of the material may vary within wide limits depending upon the particular type of rectifier or similar cold cathode tube wherein the composition in accordance with this invention may be utilized as an essential element forming the texture of the make-alive electrode. The drawing forming part of the specification, therefore, is to be taken merely as illustrative of one example of physical embodiment and application. It is not intended to limit the scope of this invention to the particular physical dimensions, contours or application shown therein.

lin constructing a make-alive electrode according to this invention, uranium oxide (U308) in powdered form may be used as the raw material. To this is added a suitable organic glue for a binder such, for example, as the gum exudate known as tragacanth, also in powdered form. The mixture then is ground for about 24 hours in a porcelain mill having porcelain balls. After the grinding operation, a small quantity of water may be added, enough to form a stiff plastic mass. The paste so obtained may then be formed into suitable shapes, such as the electrode E of Fig. 1 or rods may be made by extrusion, or in any well known manner, depending upon the physical characteristics desired for the electrode. The material so formed is allowed to dry, whereupon it is placed in a furnace and brought up to high temperatures in the neighborhood of 650 C. for approximately three hours in a hydrogen atmosphere. At the end of this time, rapid cooling thereof is effected, maintaining the hydrogen atmosphere. By this process, the uranium oxide is changed into uranium dioxide (U02) It is to be understood that theabove described method is intended merely to indicate one exam-,

ple of forming uranium dioxide bodies and any The grinding period in the porcelain mill was found to have a direct bearing on the specific resistance of the finished product and the longer the grinding operation, the lower the specific resistance of the material will become within certain limits. For example, by a 12 hour grinding period, a specific resistance of about 120 ohms per cm. can be obtained. High resistances, on the other hand, up to several megohms per cm. may easily be produced, by mixing with the powder various quantities of calcium carbonate (CaCOB) depending upon the resistance density required. Slow cooling will also increase the specific resistance.

As seen from the above, the great flexibility of the process enables a large variety of makealive electrode construction with several desirable characteristics assembled in a simple structure. In certain applications, higher specific resistance becomes the desired requisite and in others the reverse may be the case. In all, however, the characteristics exhibited by uranium dioxide and especially its negative temperature coefficient lends definite improvement to the operation of converters of the type referred to as ignitrons. The application of electrodes of this type is illustrated in Fig. 2. The rectifier I contains a cathode-pool P which is in direct contact with the make-alive electrode E.

What is claimed is:

1. In combination with vapor-arc discharge devices, an electrode of resistance material free from mercurial amalgamation in the presence of an electric arc, said material being essentially composed of a mixture of uranium dioxide and an organic binder, such as tragacanth.

2. A make-alive electrode for mercury-arc converters comprising a rod-like structure of resistance material composed essentially of uranium dioxide, calcium carbonate and organic binders.

3. In combination with an arc type converter having an anode and pool-type cathode, a low current make-alive electrode immersed therein during normal operation of said converter, said make-alive electrode consisting essentially of uranium dioxide and a small percentage of organic binders such as gum exudates.

4. In combination with an arc type discharge device having an anode, a mercury cathode, a low current igniting electrode immersed in said cathode during normal operationof said device, said electrode being composed essentially ofa mixture of uranium dioxide, calcium carbonate and tragacanth.

JOSEPH SLEPIAN. 

